Composite aluminous metal article



Jan. 28, 1958` M. A. MILLER 2,821,014

' COMPOSITE LUMINOUS METAL ARTICLE Filed May 31, 1951 '2 Sheets-Sheet 1 Jq. I.' y Y Aluminum 0120!/ v Fix/er mem iumfzum merlayep Ahzmnum all@ sru'cum member Alumina/? infer/ayer Aluminum allay filler meta! umnum all@ Srucura) member Aluminum czlqg fil/er meal Aluminum inericzyer Aluminum Mgg .Simoni/'0f member Corrosion resiszm aluminum alloy coaifzg Jan. 28, 1958 M. A.. MILLER 2,821,014

COMPOSITE ALUMINous METAL ARTICLE Filed may 31, 1951 v Y 2 sheets-sheet 2 INVENTOR` Mke. A. Mil/cr United States Patent COMPOSITE ALUMINOUS lVlETAL ARTICLE Mike A. Miller, New Kensington, Pa., assgnor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Application May 31, 1951, Serial No. 229,130

9 Claims. (Cl. 29-197.5)

This invention relates to a composite aluminous metal article designed for use in making assembled products by the brazing process. The term aluminous, as used herein, refers to both aluminum and those alloys in which that metal constitutes the major portion of the composition.

The brazing of aluminous products is a fusion joining process wherein an aluminum base alloy serves as the brazing filler metal and becomes fused while the parts being joined are not melted. In the latter respect brazing resembles soldering. The steps followed in making a brazed aluminous product consist essentially in assembling the parts to be joined in proper relationship to each other with the brazing filler metal at the interface between the parts where the joint is to be formed or at the edge of that region, so that the ller metal can ow into the interfacial space. A suitable ux is either applied to the area to be joined before any heating occurs or it may be supplied in the course of the brazing operation as in the dip brazing process. In either case, the assembly as a Whole, or only that part where the joint is to be formed, is heated to a suificiently high temperature to fuse the filler metal and permit it to establish a bond with the adjoining structural members. Following the fusion step the assembly is cooled to room temperature. The brazing process, as will be appreciated, is well adapted to forming an entire assembled product in a single operation regardless of the number or length of joints and the process may be carried out in a continuous manner, that is, the parts may be assembled and continuously fed into a furnace or bath where fusion of the ller metal is effected.

Generally, the brazing of aluminous articles is conducted within the temperature range of 1040 to 1180 F. because the most suitable aluminum base alloy ller metals melt within this range. The choice of brazing temperature employed in any particular case is usually determined by the melting point of the structural member and the brazing filler metal. Some aluminum base alloys which possess very desirable properties at room temperature cannot be heated to brazing temperatures without causing melting of some constituents while other alloys may withstand the heating but combine with the liquid brazing filler metal to form a low melting point constituent. As a result, the choice of alloys for structural members has been restricted to -very few compositions.

It has been found that although certain aluminum base alloys which contain magnesium, possess higher strengths than aluminum and the common aluminum-1.25% manganese alloys, and are able to withstand heating to the brazing temperatures without melting, they nevertheless suffer from a susceptibility to penetration by the commercial molten brazing filler metal alloys containing a substantial amount of silicon, with or without additions of copper and/or zinc. The molten metal or low melting point products formed by combination with the structural alloy member appear to penetrate the member along its grain boundaries thereby weakening-it. Thedanger-of ice penetration is especially acute where it is necessary to make brazed structures having thin walls such as found in radiators or other heat exchangers.

It is an object of this invention to provide a composite aluminous article adapted for use in making of stronger brazed assemblies. Another object is to provide a composite article having a structural member associated with a layer of brazing filler metal which can be brazed without danger of any substantial penetration of the structural member. Another object is to provide a composite aluminous article which is substantially free from penetration of the structural portion of the article by molten aluminum-silicon type alloy liller metal during the brazing operation. A further object is to provide a relatively thin composite article having a structural member associated with a layer of aluminum-silicon type of brazing ller metal that can be brazed under normal conditions without danger of perforation by the fused filler metal. Another object is to utilize aluminum base alloys containing magnesium as the structural component of a composite article in association with a layer of aluminumsilicon type brazing filler metal and yet avoid substantially any penetration by the fused filler metal during a brazing operation.

These objects and others are attained in a composite aluminous metal article wherein the structural member portion is an aluminum base alloy penetratable by fused brazing ller metal and is separated from an associated filler metal layer portion by a relatively thin interlayer of aluminum or an aluminum base alloy having a melting point above that composing the structural member. The interlayer should not be less than 0.0010 in., and preferably not less than. 0.0015 in., in thickness, and should be adhesively joined to both the structural member and liller metal layer. In particular, I have found that those magnesium-containing alloys of the aluminum-magnesium, aluminum-magnesium-silicon, and aluminum-magnesium-zinc types having melting points above about 1080 F., can be succesfully used as the structural portion of a composite article in association with a brazing tiller metal component of the aluminum-silicon alloy type and yet avoid in very substantial measure any penetration and resultant weakening of the structural member by the fused filler metal when the article is brazed if a very thin layer of aluminum or high melting point aluminum base alloy resistant to absorption is interposed between the two components and adhesively joined to each of them. In addition to inhibiting penetration the presence of the interlayer serves to promote the flow of brazing ller metal to the region of the brazed joint and thus permit the formation of better fillets because little f or none of the filler metal is absorbed by the structural member.

It is to be understood that the penetration referred to herein designates the intrusion of the structural component by the fused brazing ller metal and not a general melting of the alloy constituting the structural component. Furthermore, this penetration is not to be confused with the diffusion phenomenon in solid metals which is concerned with the migration of individual atoms from one region to another, generally in response to a dierence in concentration of the atoms in dilerent parts of the bythe-fused brazing ller metal. associated therewith.` ln;

3 particular, the structural component consists of an aluminum base alloy containing from 0.1 up to 5% magnesium, with or without the addition` of other elements providing the resultant composition does not melt below about 1080 F. and in no event below the melting point'of the brazing filler metal. Inmaking aluminum-magnesium alloys it is my preferred practice -to employifrom v025 .to 2.5% magnesium. If silicon is to be'included inthe alloy .the .amount used should be between .0.25 and 0.8% and the magnesium content Vlimited to .the range of 0.5 to V1.5 Preferably, Athe proportion of magnenesium to silicon Vshould be that found in theintermetallic compound MggSi or veryclose .tor that proportion. rfIf zincis added the amount should be less Vthanf6% but .more than .0.1% and preferably within the range of ,2.5 to. 5% while the .magnesiumcontentshould .preferably constitute 0.5 to'2.0% of theweightfof the alloy. Inaddition to Vsilicon and zinc, copper, Vmanganese and Vchromium may be employed `in the following proportions: 0.710 to 2'.0%fcopper, 0.25 to 1.5% manganese .and 0.1.10 .0.5% chromium. The copper, manganese and chromiumma-y also be `used in the absence ofsilicon and zinc. Furthermore, any `of the well-knownk grain refiningV elementsV such as titantium, boron, zirconium, columbium, :tantalum,

vanadium, molybdenum and tungstenmaybefincluded in any of the alloys .ina total amount not Yexceeding 0.5%. Beryllium may also be included inamountsof 0.005 to 0.02%.

The interlayer may be composed of aluminum.having a maximum total .iron and silicon impurity .content...of 0.8%. In V-placeof'aluminum certain. aluminum `base alloys may be employed whichzhave melting points-above that of the structural component-.alloy andfwhichsare resistant. to absorption by `the fused brazing llermetal.. Such alloys should havev a .high melting point,f..genera1ly,"

not lower lthan aboutV 11S0 F. Also, the. alloy and the aluminum should be as ine grained as possible. .Exf

amples of suitable aluminum alloys which canserve as interlayer material are aluminum-0.00510 0.10% beryl-` lium, aluminum-0.01 to 1.5 manganese andaluminum- 0.05 to 0.25% copper. designation the interlayer material may be referred toas an Valuminous interlayer resistant Vto absorption of theY ller metal since it may be composed of either aluminum,

or a suitable aluminum base alloy. V V

The. brazing. filler metal component of :thecomposite article;shou1d consist of any, suitable Valuminumabase alloy having a sucientlyvlow melting point, Vthemetal ow characteristics and other qualities essential tov forming.

asatisfactory brazed joint. VIn general, .aluminumbase alloys containing 5 to 15% silicon, with Aor 'withontfadditions of. 1 v.to 10% Yzinc or 0.2.to 5%. copper, or both, :are very satisfactory. .It is .to be 'understood .that other 'metals suchas nickel, germaniumand magnesium-.maybeV-added to.;Venhance .certain .properties yof theiiillenmetalfalloy sheet lhaving no interlayer which .had been heatedto"V brazing temperature; Eig. v5 isVa photomicrograph .at .the

samemagm'ication of asectionf'ofa similar sheet with an interlayer heated to the same temperature; Fig..f.6,:is Fa'. photomicrograph, :at a 'magnication of. .100 diameters, of "a section of a brazedT .joint vwheremo.interlayer was present and Fig. 7 is a photomicrograph at..'the;same.

magnification of a similar .section of a `Tjoint where an interlayer was present.

As' indicated :by 'fthe legends 'in Figs.

aluminum 'interlayer .inthecomposite .sheets separateslilhe.:

For the purpose of .convenient aluminum alloyA structural members from the aluminum base'alloy brazingfiller metal layer and is co-extensive with the ller metal. The'composite sheet may have but one structural member, as in Fig. l, covered on one side by an interlayer and associated brazing filler metal, or the ller metal layer may be placed between two structural members with intervening interlayers as shown in Fig.,2. .The threelayer sheetshown in Fig. .-1Y may. be modified bythe addition of a corrosion resistant coating Aofi aluminum-.f orl aluminum baseall'oy.4` as 'zillus'tratedrf in.' Fig-3. VSuch afourlflayerfsheetis of specia'l'value-where one side of the article in service `is.` in 'contactu'ith-La corrosive-,duid as.innadiatorsor.other heatexchangers. An alloy layer having other characteristics than resistance to corrosion suchasdnigherf-zhardness, Wear resistance or other properties may be substituted for the fourth layer. Itwill be understood that other combinations and. .arrangements .of-thethree essentialomponents: may be made as. long al?A interlayer of .adequate .thicknessseparates the ,fillermetalfromthestructural member.

-:.Figs. 4,' 5,6 andshow theappearance of a. portion .of

a typical .cross section, including-the brazing filler. metal surface, of similar composite sheets of aluminum-1.2%v

magnesiunrand` aluminum-10% siliconf alloys afterv the sheets were .'.subiected to .brazingl fconditions. Y.In f each caseftheTcQmPoStesheet.was0.064 in thickness. The

alnminumfsilicon ...alloy r layer constitutedfabout 10.5 V

of the rectal;thicknesssofnthe. crunposite sheetwhi1ethel aluminuminterlayer.seenyinligsfj.and 7, was 0.00238" `in',.thicknessf.aridrepresented4% Vof* thetotal thickness.

Thelsheets. ilhistrated--infligs.-f4and .i5 wereplaced infza horizontalgpositiou;withthe fillermetal on top, in a. circu- .l latingfair furnaceheated. to.:l 120 .'F.sheld for 42 minutes inithe furnace,eremovedqandxooledto room .tempera-l ture thus V. simulating conditions .prevailing lin yfurnace hrazingpractice. begseenfin Eig.- 4Y that-.the fused aluminum-.silicon falloywfhas, penetrated the' aluminum-V magnesium alloy-frnernberK along f grain I boundaries V`to a depth'rabout e.qnal.=,to-..that.zof the original filler :metal layer. The penetration aproducedv al brittle,V low Ymelting point `constituent.thathad .an-:adverse yeffect l`upon. 'the properties of.,-.the zbrazed product In l.contrast V-to ethe.

conditionseensin Fig.4.is2fthatfillustratedinfFigfS where.

the V-faluxx'iirmm interlayer prevented any penetration of'Vthetstructurakmember.- V V Figsnzand /ushowfthc sameacomposite sheet.materialsV whenrnsedtoffform-mr. brazed '-l :joint with, asheet fofr .aluminima. "Ihenccmpo'site-:sheetse members were assembled in an inverted T shaperthe composite.;.shcet bcingrin fyertical .position `with the `aluminumsheet at theibottom vIlhe :assembly was immersed. Vcouveauticuialf.fused salt uxbathzheld for12 minutes-:inn

Y atzaitempcratureieof f1 1'20'.FV. f'AtVthe .endof that period thenassenibly-fwasvwithdrawn.and cooled to Vroomtemperature. monly used infhrazingfbylthe dip'method. Thepenetra-V tionzofvthe :structuralimemberfisfevidentinFign `and .the Y no;.ller `.metal 5wasV lost bygpenetration `'of .the .aluminum-- [firmlybondedatheretofandrtothebrazing.llenmetallayenl .Jhetnluminous interlayermustbcover; atlcstgagportiort d .the aluminum. cross This :.operat-ion r.; followed Y the l:practice com.,V

of the surface of the structural member and the filler metal layer must not extend beyond it if penetration of the structural member is to be avoided.

Moreover, the interlayer, ller metal and structural component may be arranged in any sequence or order as indicated in Figs. l, 2 and 3. Although there may be two or more structural members ot a composite article, all of them are collectively referred to herein as a structural component. The specific arrangement of the several parts is a matter of choice depending upon the ultimate use of the composite article.

Where a corrosion resistant alloy is employed as a fourth component, a number of known compositions may be used such as described in U. S. Patents 1,997,165 and 1,997,166 providing the melting point is high enough to avoid melting at brazing temperatures.

. The total thickness of the composite article can be varied according to the requirements of the brazed assembly. Ordinarily, when in the form of sheet, the total thickness is not likely to exceed about 0.100", however, the article will have a greater thickness if the structural member is a plate, rod, forging or casting. In any case the brazing ller metal should constitute but a relatively small part of the total cross sectional thickness of the article inasmuch as only a small amount is required to supply metal for the brazed joints. The thickness of the layer for any given composite article, will be determined by the amount needed to form a joint with proper fillet. Generally, a layer or coating which constitutes from 5 to 20% of the total thickness of the article is adequate if the structural member is a sheet or plate or of a thickness equivalent to sheet or plate.

' The aluminum interlayer should be thick enough to prevent any substantial penetration to the structural member by the fused brazing ller metal under normal brazing conditionsbut under no circumstances should the thickness be less than 0.001 in., and preferably not less than 0.0015 in., since a thinner layer does not afford adequate protection. Furthermore, it need not exceed of the total thickness of the composite article. In most cases the interlayer should be thinner than the adjoining ller metal layer and usually should constitute from 2 to 10% of the total thickness of the article. The structural member or members or layer of other aluminum base alloy Should comprise the remainder of the composite article and generally this amounts to 60 to 95% of the total thickness.

The effectiveness of the interlayer is very surprising in view of its extreme thinness. For example, if molten aluminum-silicon alloy, within the brazing temperature range, is brought into contact with ordinary aluminum foil, of say 0.002 to 0.003 inch in thickness, coated with a brazing flux, the liquid metal will very quickly alloy with and absorb that foil within a period no longer than that employed in forming a brazed joint. However, an interlayer of aluminum of the same or lesser thickness in a composite article as herein defined, in the presence of the same iluX at the same temperature and within the same period of time, will not be completely absorbed by the fused aluminum-silicon type alloy. The reason for this difference in performance is not clear, but there is no doubt about the eiectiveness of the interlayer is protecting the structural component.

The protective aluminous interlayer is adhesively joined to the structural component in any known manner providing it becomes rmly attached thereto, preferably by means of a metallurgical bond. The best results are obtained if an integral bond is established under the inuence of heat and pressure. Thus, the aluminum or proper aluminum base alloy in sheet or plate form may be rolled or pressed onto the base component, if the shape permits it. Also, a duplex ingot may be produced by casting the strutcural alloy against a 'slab of aluminum or aluminum base alloy, or, the reverse procedure may be followed if proper thermal conditions are created and the composite ingot worked to the desired shape. In some cases, a sprayed aluminous coating may be found to be satisfactory, especially if subsequently compacted on the underlying metal. Application of the coating by casting or spraying is particularly suitable where the structural member is a casting.

The brazing filler metal layer may then be adhesively joined to the aluminous coated structural member according to any of the procedures described above. While it is possible to apply each layer successively as has been mentioned, it is generally more economically in the case ot' sheet and plate to provide the filler metal layer with the desired aluminous coating on one of two sides, depending on character of thc composite article, and then bond it to the structural component under the inuence of heat and pressure. Thus, the ller metal body can be rolled to slab dimensions and the aluminous interlayer material applied thereto by a hot rolling operation. The method of forming the composite article, it should be understood, does not constitute a part of my invention.

'lhe advantages of employing an aluminous interlayer in a composite article are illustrated in the following examples in which different alloys were used as structural members. The nominal composition of the several alloys is listed in Table l.

TABLE I Percentage composition of structural member alloys lwn The composite samples used in the first series of tests consisted of sheet 0.064" in thickness. In all cases but the last two, a brazing filler metal of an aluminum-10% silicon alloy was present on one side of the structural member. In the last example involving alloy E, the brazing ller metal consisted of an aluminum-7.5% silicon alloy which was present on both sides of the core member. The samples were prepared by rolling the components together and thus establishing a firm bond between them. Half of the samples contained no aluminum interlayer while the balance had such an interlayer between the filler metal and structural member. The test consisted of heating the samples to 1120 F. for a period of 2 minutes followed by cooling in air to room temperature to simulate the conditions prevailing in brazing operations. The samples were microscopically examined to determine the average penetration of the structural member by the filler metal. The thickness of the interlayer, the ller metal layer and the average penetration of the structural member brought about by heating are given in Table II below.

TABLE II Penetration of structural member Thickness Percent Thickness Percent Average Structural of lnterof Total of Filler of Total Penetra- Alloy layer, Thick- Metal, Thicktion,

Inches ness Inches ness Inches None 0 0. 00784 12. 2 0. 0042 0. 00224 3. 5 0. 00784 12. 2 0. 0000 None 0 0 00672 10. 5 0. 0075 0. 00238 4. 0 0. 00672 10. 5 0. 0000 None 0 0. 0068 10. 6 0. 0056 0. 0051 8.0 0.0072 11. 2 0. 0000 None 0 0. 0070 10. 9 0. 0017 0. 0053 8. 8 0. 0070 10. 9 0. 0000 None 0 0. 005 7. S 0. 0052 (each side) 0. 0023 3. 6 0. 005 7. 8 0. 0000 (each side) (each side) lt is apparent that the interlayer completely prevented the penetration of the structural member by the fused e7 lllermetal. The microscopic lappearance:ofia cross sec;-` tion ofA thegsamples involving ,structural a1 loy.B maybe Seen `in Biss-flfaridS- 1 The penetration referred to .aboveis not only evident upon-microscopic.examination but'its elect isalsorevealed in the reduced elongation values of ...the heated` compositesheet. This is illustrated bythe tensiletest reslts obtained ona portion ofthe material listed .in Table IIfunder the structural alloys A,Y.B, C.and E. .Theproperties yofthe -sheethaving alloy Easacomppnent were obtained `4weksafter bieingvheatedftorthe brazing temperature; 'Y Y TABLE III Tensile y properties. of -heated-composite sheet The low elongation Values of the samples having no interlayer,` reveal the: very 1 pronounced .J- effect JofY partial penetration of `thestructnralmembersand that the intergranular penetration: shown invFigs. 4 and16 :embrittles the--a-luminnm-magnesiumalloys. Theincreased-strength exhibited by. examples. ofB, C .and E alloys having interlayerrs is'alsofindicative'of an advantage-that-may-be gained in. some iustanceslby preventing penetrtionf tle structuralmember; W 'f The thickness Vof the aluminum 'interlayerrhasian important bearing -upon penetration-10i the Astructural memberof a composite sheet. This is 4to be seen inthe followingv examples lWhere a ve .componentisheetwas usedas illustrated in Fig. 2. V:The vstructural"members werercomposed i; f: al1oy"E and therllermetal consisted of @aluminum-13% silicon alloy. vThe composite-sheet in eachcase'had a total thickness of 0.064", butthethick-nessiofV the'interlayer'was-varied. The composite sheet fsampleswerev brazed to ian--`aluminum base in the. form ofV a' TV joint by -immersingtheT assembly for a 2 minute. period in a` fusedl salt flux? bath: maintained atfa temperature offl 100 i-F. "The thickness ofthe interlayer, filler metal and average-penetration of the structural member are given below 'in'Table IV.

TABLE 1v y p :Effect of thickness 'ofnterlayer on penetration Thickness of Inter- Thickness of Filler layer Metal Average 'Penetra- Percent Percent tion, Inches of Total Inches A ot Total Inches Thie'k- Y Thickness ness 0. 0002 3 0. 0047 7. 3 0. 0045 0. 0007 1. 1 0. 0047 7. 3 0.0021 0. 0026 4'. I 0. 0046 7. 2 v0. 0000 0. 0036' 5.V 6 0. 0045 7. 1 0. 0000 65 said. interlayerfcomposed ogfzanaluminum base alloy hav-,-

present `in thelayerpn .thefcompositeshcet prior-.to heat ing and thel vlinef ofthe vrntfalI in ,the 'llet offfthe joint following heating.' The?,prcnt'avgeof thejnitial volumfe; of .the .llermetalfound in. the. fillet Awas consideredto be a niesu're of theangunt :of fowhathad. takenplace. The,resilltstifthesel tests` are givenbelow-.inlablel Elow of ller metal .t

PercentFlowoiIiller 5 Sheet f Metal Structural lAlloy Thickness, l

Y Inches l Y "'No'Interf WithInterllayer layer t 0.012 V- 62 0.064 '35 57 0.012 '34 T 0.064 37 v.47. 05064 VV(l The vbeneiit from of-theV laluminum interlayer .ezt-l tends over..a.range.offbraaingtemperatures as demon-A; strated by.: thettalloWingeXamples of 0.064 .thick cornf4l positesheet made-with alloy Egas the structural member.,

A Both 4sides of' the .memberwere.` 'covered with. an aluminum-`7.5%gsiliconvflayer, v0.005" in thickness. The Aalu-y mium interlayerY was'4 0 .00237A in thickness o'r 3.6%. of. the, total ythickness yof the composite sheet.y .Thesamples were` 'heated for twominutes at the temperaturessindicatedin heating the samples Were .coole d in air to room-tempera-l ture. .The penetration and owofllermetalare .given inable. VI below- A Having thus .described my invention and' certain embodiments thereof, I claim:

1. :A composite aluminous metal article adaptedtobe joined to another=metallc-body by thebrazing process, said article having .-agrstructuraltcomponent consisting; ofan aluminumbase alloythat hasameltinggpointfnoh lowerthan 108051:: amis-susceptible tolpenetration. by molten brazing illerfmetalya aluminous interlayexj,Y at least 0.0010" inand constitutingl from 2.10.I 10%y of thetotal thicknessfofrthe compositerarticle, .said intel-layer vextending'ovwerat. least a portion of Ithe surface of said structural componentad tadhesively joined .-there, to, saidlinterlayer also.havingy a melting pointnot lower. than 1180 F. Vand above that 1ofthestructuraLcolnpQnent; and a layer.: of' .brazipg filler metalV adhesively joined :'-to

ing .a' melting p cintbelow that off-the structural com Y ponent, saidbrazing pillerlmetal beingzcompletelyf.sep-E aratedafrom-saidtstructural corinponenty by said nterlayer, said. .composite anticle being characten'zed. by substantial` freedom fromjfPenetrationxzof the .structural .,COmpQnnl'.:

Said artlhving a structural'component consisting analuminum base alleyeomaining 0.1 to" 5% magnesiunt gesamt as the essential added alloy component and the balance substantially aluminum, said alloy having a melting point not lower than l080 F. and susceptible to penetration by molten brazing filler metal; a thin aluminous interlayer at least 0.0010" in thickness and constituting from 2 to 10% of the total thickness of the composite article, said interlayer extending over at least a portion of the surface of said structural component and adhesively joined thereto, said interlayer also having a melting point not lower than ll80 F. and above that of the structural component; and a layer of brazing ller metal adhesively joined to said interlayer composed of an aluminum base alloy containing from 5 to 15% silicon as the essential added alloy component and the balance substantially aluminum and having a melting point below that of the structural component, said brazing ller metal being completely separated from said structural component by said interlayer, said composite article being characterized by substantial freedom from penetration of the structural component by molten filler metal during the brazing process.

3. A composite aluminous metal article adapted to be joined to another metallic body by the brazing process, said article having a structural component consisting of an aluminum base alloy containing 0.5 to 1.5% magnesium and 0.25 to 0.8% silicon as the essential added alloy components and the balance substantially aluminum, said alloy having a melting point not lower than 1080 F. and susceptible to penetration by molten brazing iiller metal; a thin aluminous interlayer at least 0.0010" in thickness and constituting from 2 to 10% of the total thickness of the composite article, said interlayer extending over at least a portion of the surface of said structural component and adhesively joined thereto, said interlayer also having a melting point not lower than ll80 F. and above that of the structural component; and a layer of brazing filler metal adhesively joined to said interlayer composed of an aluminum base alloy containing from 5 to 15% silicon as the essential added alloy component and the balance substantially aluminum and having a melting point below that of the structural component, said brazing filler metal being completely separated from said structural component by said interlayer, said composite article being characterized by substantial freedom from penetration of the structural component by molten filler metal during the brazing process.

4. A composite aluminous metal article adapted to be joined to another metallic body by the brazing process, said article having a structural component consisting of an aluminum base alloy containing 0.5 to 2.0% magnesium and 2.5 to 5.0% zinc as the essential added alloy components and the balance substantially aluminum, said alloy having a melting point not lower than S0 F. and susceptible to penetration by molten brazing ller metal; a thin aluminous interlayer at least 0.0010" in thickness and constituting from 2 to 10% of the total thickness of the composite article, said interlayer extending over at least a portion of the surface of said structural component and adhesively joined thereto, said interlayer also having a melting point not lower than 1180 F. and above that of the structural component; and a layer of brazing iiller metal adhesively joined to said interlayer composed of an aluminum base alloy containing from 5 to 15% silicon as the essential added alloy component and the balance substantially aluminum and having a melting point below that of the structural component, said brazing filler metal being completely separated from said structural component by said interlayer, said composite article being characterized by substantial freedom from penetration of the structural component by molten iiller metal during the brazing process.

5. A composite aluminous metal article adapted to be joined to another metallic body by the brazing process, said article having a structural component consisting of an aluminum base alloy containing 0.1 to 5% magnesium and 0.25 to 1.5 manganese as the essential added alloy components and the balance substantially aluminum, said alloy having a melting point not lower than l080 F. and susceptible to penetration by molten brazing ller metal; a thin aluminous interlayer at least 0.0010" in thickness of the composite article, said interlayer extending over at least a portion of the surface of said structural component and adhesively joined thereto, said interlayer also having a melting point not lower than 1l80 F. and above that of the structural component; and a layer of brazing filler metal adhesively joined to said interlayer composed of an aluminum base alloy containing from 5 to 15 silicon as the essential added alloy component and the balance substantially aluminum and having a melting point below that of the structural component, said brazing filler metal being completely separated from said structural component by said interlayer, said composite article being characterized by substantial freedom from penetration of the structural component by molten iiller metal during the brazing process.

6. A composite aluminous sheet metal article adapted to be joined to another metal body by the brazing process, said article having a structural component consisting of an aluminum base alloy that has a melting point not lower than 1080 F. and is susceptible to penetration by molten brazing filler metal, said structural component also comprising from 60 to 90% of the total thickness of said composite sheet; a thin aluminous interlayer of at least 0.0010 in thickness and constituting from 2 to 10% of the total thickness of the composite article and extending over at least a portion of the surface of said structural component and adhesively joined thereto, said interlayer having a melting point not lower than 1180 F. and above that of the structural component; and a layer of brazing filler metal adhesively joined to said interlayer composed of an aluminum base alloy containing from 5 to 15% silicon as the essential added alloy component and the Ibalance substantially aluminum and having a melting point below that of the structural component, said layer of brazing filler metal compr-ising from 5 to 20% of the total thickness of the composite article, said brazing ller metal layer also being completely separated from said structural component by said interlayer, said composite sheet metal article being characterized by substantial freedom from penetration of the structural component by molten ller metal during the brazing process.

7. A composite aluminous metal article adapted to be joined to another metallic article by the brazing process, said article having a structural component consisting of an aluminum base alloy that has a melting point not lower than 1080J F. and is susceptible to penetration by molten brazing ller metal; a thin aluminous interlayer at least 0.0010 in thickness and constituting from 2 to 10% of the total thickness of the composite article, said interlayer extending over at least a portion of the surface of said structural component and adhesively joined thereto, said interlayer also having a melting point not lower than 1180 F. and above that of the structural component; a layer of brazing filler metal adhesively joined to said interlayer composed of an aluminum base alloy having a melting point below that of the structural component, said brazing filler metal being completely separated from said structural component by said interlayer; and a corrosion resistant aluminum base alloy layer adhesively joined to the opposite side of said structural component, said corrosion resistant alloy containing as the essential added alloy component at least one element which raises the solution potential of the alloy above that of aluminum, said component article being characterized by substantial freedom from penetration of the structural component by molten iller metal during the brazing process.

8. A composite aluminous metal article adapted to be joined to another metal article by the brazing process, said article consisting of live members in layer-like relationship to each other, a central brazing ller metal layer asesora 1-1 composed of an aluminum base alloy ,having .a ,melting pointlb'elow that of 'the Structural ime'mbersgjaf thm aluminous interlayer adhesivelyjj joined to jbothf sdesof'j said-ll'ler metal-layer, said interlayer having ',ameltngj point not lower than 1180" and above Ithat ofthe struc' tural components, Veach interlayer having 'athickness'o'f at least 0.0010 in thickness and constituting`from"2 to 10% of the total thickness of the composte'jartile, andl a structural member joined to eachlinterlaver, saidstruc-j tural member consisting of an aluminumfbasesalloy which has a melting point not-lower'than'10S0F.1and^is vsus-K` 'ceptible' to penetration bymolten brazing llerrnetal'inL the` absence of the aforesaidinterlayer, saiclY composite article being .characterized `by substantialfreedomrom penetration of the `structural component bysthefmolteln? iller metal 'during the brazing'pro'cess.

9. A composite aluminousmetall article adaptedtobe joined to another metallic Vbodysbyfthe brazingv process, said article Vhaving a' structural componentconsistingfof an aluminum base'alloycontaining from 0.1 to 5%-nxag-A nesium as an essential jadded alloy component and the balance substantially aluminumssaid alloy havingaumelting point not lower than 1080'F.; a thinaluminous lmetal interlayer composed of 4metal of the fclass'A consisting of aluminum and an aluminum base alloy composed yof aluminum and. at least one of -themetals beryllium-, manganese and'copper irrthe proportionof 0.0051to`0.1%V beryllium, .0.01 to 1.5% manganese and 0.05A to 0.25% copper, saidinterlayer having .a'thickness of at least R1 andtabove thatH of the structural componente and a' layer of brazing'ller metal adhesivelyjoined 4to said inter-f layer composed of an aluminumbase'alloy containing from MSto 15% silicon as-'the'essential-addedalloy'com ponent vand the balancefsubstantially aluminum yand-fhav-' ing afmelting pointl below-that of the Vstructural cornponent, saidk brazing ller metal beingwcompletely-'sepa rated from the structurall component hyf-y said inte11ayer-,V said composite -article being`Y characterized by asulavstan'-,I

tial :freedom from `penetration of- Mthe--str ucturalcima? f DixV s vrun2s, 1129,32 

1. A COMPOSITE ALUMINOUS METAL ARTICLE ADPATED TO BE JOINED TO ANOTHER METALLIC BODY BY THE BRAZING PROCESS, SAID ARTICLE HAVING A STRUCTURAL COMPONENT CONSISTING OF AN ALUMINUM BASE ALLOY THAT HAS A MELTING POINT NOT LOWER THEN 1080*F. AND IS SUSCEPTIBLE TO PENETRATION BY MOLTEN BRAZING FILLER METAL; A THIN ALUMINOUS INTERLAYER AT LEAST 0.0010" IN THICKNESS AND CONSTITUTING FROM 2 TO 10% OF THE TOTAL THICKNESS OF THE COMPOSITE ARTICLE, SAID INTERLAYER EXTENDING OVER AT LEAST A PORTION OF THE SURFACE OF SAID STRUCTURAL COMPONENT AND ADHESIVELY JOINED THERETO, SAID INTERLAYER ALSO HAVING A MELTING POINT NOT LOWER THAN 1180*F. AND ABOVE THAT OF THE STRUCTURAL COMPONENT; AND A LAYER OF BRAZING FILLER METAL ADHESIVELY JOINED TO SAID INTERLAYER COMPOSED OF AN ALUMINUM BASE ALLOY HAVING A MELTING POINT BELOW THAT OF THE STRUCTURAL COMPONENT, SAID BRAZING FILLER METAL BEING COMPLETELY SEPARATED FROM SAID STRUCTURAL COMPONENT BY SAID INTERLAYER, SAID COMPOSITE ARTICLE BEING CHARACTERIZED BY SUBSTANTIAL FREEDOM FROM PENETRATION OF THE STRUCTURAL COMPONENT BY MOLTEN FILLER METAL DURING THE BRAZING PROCESS. 